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UNIVERSITY   OF   CALIFORNIA  agricultural  Experiment  Station 

College  of  Agriculture  e,  w.  hilgard,  director 

BERKELEY,   CALIFORNIA 


CIRCULAR  No.  7. 

(June,  1903.) 


REMEDIES  FOR  INSECTS 


By  C.  W.  WOODWORTH. 


[The  demand  for  information  relative  to  the  destruction  of  injurious  insects  has  been 
an  important  part  of  the  correspondence  of  the  Experiment  Station.  To  assist  in 
answering  these  letters  of  inquiry,  there  was  issued,  in  1893,  a  circular  giving  the 
formulse  of  the  standard  remedies.  The  edition  was  soon  exhausted,  and  a  more 
elaborate  treatment  of  the  subject  was  prepared  and  issued  as  Bulletin  No.  115.  This 
likewise  did  not  last  long,  and  was  reprinted  in  the  report  for  1895-97,  and  a  considerable 
edition  of  the  article  was  printed  separately.  The  formulse  were  also  again  printed  in 
circular  form.  The  present  circular  is  a  second  revision  of  Bulletin  No.  115,  omitting 
the  parts  relative  to  fungous  troubles.] 

It  is  very  important  that  every  one  who  has  the  care  of  crops,  whether 
of  garden,  orchard,  or  field,  should  have  a  clear  idea  of  the  remedies 
available  for  preventing  the  injuries  due  to  insects.  Not  only  must  one 
know  how  to  make  and  apply  the  remedies,  but  it  is  equally  essential 
that  he  should  fully  understand  when  to  apply  and  when  not  to  apply. 

This  will  involve  a  certain  knowledge  of  insects  and  fungi,  but  not 
necessarily  the  knowledge  of  species  nor  of  structure  which  is  generally 
designated  by  the  term  entomology.  What  is  needed  is  a  clear  appre- 
ciation of  the  nature,  time,  and  extent  of  the  injuries  produced  by  the 
various  forms  of  organisms  attacking  the  plants,  and  of  the  degree  of 
immunity  which  may  be  afforded  by  the  use  of  the  remedies  at  our 
disposal. 

The  farmer  should  clearly  understand  that  the  use  of  remedies  is 
purely  a  matter  of  dollars  and  cents.  Money  or  time  should  only  be 
invested  in  this  work  when  there  is  good  prospect  of  an   ample  return. 

It  is  safe  to  say  that,  even  in  California,  where  this  matter  has  been 
agitated  for  so  many  years,  in  only  a  very  small  fraction  of  the  cases 
where  injury  might  be  prevented  is  the  proper  treatment  made.  It  is 
very  difficult  to  estimate  the  amount  of  preventable  loss  that  occurs  in 
this  State  every  year,  but  it  is  an  entirely  conservative  estimate  to  say 
that  it  amounts  to  hundreds  of  thousands  of  dollars.  On  the  other 
hand,  it  may  also  be  said  that  when  a  treatment  is  made  it  is  often  of 


2  — 


no  effect,  and  is  a  waste  of  time  and  money.  Careful  observation  of  the 
practices  in  this  State  in  reference  to  treating  insects  makes  it  appear 
that  fully  half  of  what  it  now  costs  to  treat  our  crops  is  wasted. 

The  remedy  for  this  condition  of  affairs  is  only  to  be  found  in  the 
farmers  of  this  State  becoming  better  informed  in  regard  to  these  things. 
Heretofore,  too  many  have  blindly  followed  receipts  or  prescriptions 
which  may  have  applied  only  to  a  particular  case;  and  often  when  the 
results  were  not  satisfactory  they  have  given  up  hope  of  doing  any- 
thing and,  pocketing  their  losses,  have  blamed  the  weather.  Most  of 
the  knowledge  necessary  to  enable  the  farmer  to  do  this  work  intelli- 
gently is  to  be  had  only  by  observation,  for  everything  depends  on 
conditions  which  one  must  learn  to  recognize. 

This  article  has  been  prepared  with  the  desire  of  directing  the  atten- 
tion of  the  farmer  to  those  things  which  it  is  necessary  for  him  to 
consider  in  deciding  on  a  treatment,  and  to  furnish  the  necessary 
information  as  to  the  means  of  such  treatment. 

Mistakes  Made.—  The  chief  mistakes  made  in  applying  remedies  for 
insects  are  the  following: 

First— Applications  are  often  made  when  there  is  absolutely  no  need 
for  treatment— when  there  is  nothing  to  destroy  or  to  prevent. 

The  majority  of  people  have  now  given  up  the  practice  of  taking 
medicines  unless  they  are  sick;  but  many  of  our  most  progressive 
orchardists  consider  it  a  mark  of  advanced  farming  to  treat  their  trees 
with  religious  regularity,  whether  they  show  distress  or  not.  There 
may  be  localities  where  the  presence  of  a  certain  insect  makes  such 
regular  treatments  useful,  and  we  have  nothing  to  say  against  such  pre- 
ventive treatments  when  there  is  something  to  prevent,  but  are  only 
condemning  a  very  common  practice  in  cases  where  the  treatment  is 
absolutely  useless. 

Second— Applications  are  often  wrongly  timed;  either  applied  before 
there  is  any  chance  to  produce  good  results,  or  after  the  injury  has  been 

done. 

Our  attention  has  been  called  to  not  a  few  cases  of  a  winter  wash 
having  been  applied  to  apple  trees  as  a  remedy  for  codling-moth.  The 
time  might  as  well  have  been  spent  in  whitewashing  the  fence,  so  far  as 
any  effect  upon  the  insect  is  concerned;  indeed,  it  now  appears  that,  at 
least  in  many  parts  of  the  State,  the  first  treatment  in  the  spring  might 
as  well  be  omitted.  It  is  commonly  true  that  a  plant  affected  in  any 
way  will  look  its  worst  at  about  the  time  that  the  injury  ceases,  and  at 
this  time  it  is  no  uncommon  thing  for  an  unobservant  man  to  apply  a 
remedy;  and  no  matter  what  is  applied  if  he  remains  equally  unob- 
servant he  will  think  he  has  found  a  cure.  This  explains  many  of  the 
recommendations  honestly  made  by  honest  men  of  remedies  entirely 
useless. 


—  3  — 

Third— Often  the  wrong  kind  of  an  application  is  chosen  for  the 
particular  trouble,  so  that  no  results  can  follow. 

The  use  of  paris  green  for  sucking  insects  is  one  of  the  commonest 
mistakes.  The  number  of  kinds  of  treatments  which  are  now  recom- 
mended by  the  best  authorities  is  not  large,  and  the  purposes  for  which 
they  may  be  used  are  very  distinct  and  easily  understood,  and  it  does 
not  seem  that  there  is  any  excuse  for  making  this  mistake. 

Fourth — Applications  are  often  made  for  troubles  that  are  incurable 
by  any  known  method. 

It  too  often  occurs  that  a  person  will  go  on  year  after  year  making  a 
treatment  and  not  give  one  moment's  attention  to  the  results.  No 
treatment  should  ever  be  made  without  careful  observation  to  determine 
the  results.  Without  this,  one  will  often  go  through  the  motions  with- 
out accomplishing  anything. 

Fifth — Expensive  methods  are  employed  when  cheaper  ones  will 
accomplish  the  results  as  well,  both  as  regards  the  material  used  and 
the  labor  employed. 

Under  this  head  there  will  be  condemned,  practically,  all  of  the 
proprietary  mixtures  on  the  market.  There  is  nothing  sold  that  is 
more  efficacious  than  the  remedies  recommended  in  this  article;  and  to 
pay  more  for  a  secret  remedy  just  because  it  is  well  advertised,  is  simply 
paying  for  that  advertisement.  Many  of  the  secret  remedies  are  good 
and  effectual,  but  cheapness  is  a  matter  that  should  not  be  overlooked. 

In  the  matter  of  labor  there  is  at  present  a  great  amount  of  waste, 
and  this  is  especially  true  with  summer  washes.  No  more  time  should 
be  spent  on  a  tree  in  applying  summer  sprays  than  is  necessary  to 
thoroughly  wet  it,  and  if  it  is  allowed  to  drip,  too  much  has  been  put 
on.  The  amount  of  time  necessary  to  cover  a  certain  area  can  be  readily 
determined  by  spraying  against  the  side  of  a  shed  where  the  wetness 
will  show;  and  one  that  has  not  tried  it  will  be  surprised  how  rapidly  it 
may  be  done.  For  any  but  wTinter  washes  the  truck  or  wagon  need  not 
stop  at  all  while  the  spraying  is  being  done,  and  those  manipulating 
the  nozzle  should  ride.  The  labor  in  spraying  should  be  the  least  item, 
while  now  it  is  generally  the  largest. 

Sixth — The  ingredients  of  remedies  as  purchased  are  frequently  of 
poor  quality. 

This  may  occur  as  the  result  of  the  dishonesty  of  the  dealer,  but 
more  often,  perhaps,  because  of  the  desire  of  the  purchaser  to  obtain  a 
cheap  article  regardless  of  quality.  It  is  essential  that  the  purchaser 
insist  on  receiving  good  chemicals,  or  his  money  and  labor  will  be  in 
vain. 

There  is  no  reason  why  these  mistakes  might  not  to  a  greater  degree 
be  avoided.  Mistakes  of  judgment  will  also  cause  loss  in  this  as  in  any 
other  operation,  but  there  is  no  reason  why  those  due  to  ignorance 
should  be  allowed  to  amount  to  half  the  cost  of  such  applications. 


In  the  following  pages  we  will  attempt  to  present,  in  a  brief  compass, 
the  more  important  points  to  be  considered  in  the  treatment  of  insects. 
But  it  should  be  distinctly  recognized  that  local  experience  and  experi- 
ment are  the  only  real  guides  for  successful  practice.  Especially  in  this 
State,  where  our  conditions  are  so  wonderfully  diversified,  it  is  impossible 
to  formulate  detailed  programs  or  calendars  of  operations  which  will  be 
of  general  value. 

Any  one  with  ordinary  intelligence,  however,  who  is  willing  to 
observe  and  think,  has  no  excuse  for  falling  into  the  mistakes  indicated 
above. 

CLASSES   OF  PESTS. 

The  serious  insect  pests  that  attack  plants  we  may  classify  according 
to  their  way  of  attacking  the  plant,  into  a  number  of  groups,  as  follows: 

1.  Root-feeding  insects,  which  attack  the  roots  of  plants;  they  may 
devour  the  roots,  suck  the  sap,  or  cause  swellings  to  form;  and  the  same 
insect  may  even  attack  the  plant  above  ground  as  well  as  on  the  roots. 

2.  Boring  insects,  which  live  within  the  plant  and  mostly  attack  the 
stem  or  trunk,  but  may  also  bore  into  the  larger  roots  on  the  one  hand, 
and  into  the  interior  of  leaves  and  fruit  on  the  other. 

3.  Sap-sucking  insects,  which  attack  the  upper  parts  of  the  plant, 
puncturing  the  leaves  and  stems  to  obtain  their  food.  These  resemble 
the  forms  that  suck  the  sap  from  the  roots,  but  the  latter  are  a  different 
and  much  more  difficult  economic  problem. 

4.  Defoliating  insects,  which  eat  the  leaves  and  other  green  parts  of 
plants. 

ROOT-FEEDING    INSECTS. 

Fortunately  the  number  of  root-feeding  insects  is  not  large,  for  there 
is  no  application  known,  that  is  practical  for  general  use,  by  which 
they  can  be  treated.  It  is  not  that  the  insects  are  hard  to  kill,  but  that 
the  nature  of  the  soil  is  such  that  it  is  very  difficult  to  reach  them. 

A  large  number  of  remedies  have  been  proposed  and  tried.  A  majority 
of  them  consist  in  dissolving  in  the  water  of  the  soil  some  substance  fatal 
to  insect  life.  The  substance  is  sometimes  applied  dry,  like  a  fertilizer, 
and  subsequently  dissolved  by  the  rains  or  by  water  applied  to  the 
ground;  or  sometimes  a  solution  of  the  substance  is  poured  over  the 
ground.  Another  class  of  remedies  contemplates  filling  the  air  spaces 
in  the  soil  with  a  poisonous  vapor.  A  third  class  of  remedies  are  those 
intended  to  suffocate  the  insects  by  removing  the  air  from  the  soil;  this 
is  generally  accomplished  by  filling  the  soil  with  water.  Finally,  the 
plan  has  often  been  tried  of  penetrating  the  soil  with  something  dis- 
tasteful to  the  insects  in  order  to  drive  them  away. 

The  last  class  of  remedies  has  been  very  attractive  to  many  people, 
but  no  one  has  yet  found  any  substance  that  is  so  distasteful  to  any 


)T\ 


insect  as  to  produce  practical  results.  The  other  three  classes  are  more 
or  less  effectual,  and  especially  the  use  of  water.  The  great  amount  of 
water  necessary,  however,  makes  it  impracticable  except  under  very 
favorable  circumstances.  Of  the  others  the  best  known  process— the  use 
of  carbon  bisulfld — is  not  certainly  effectual,  unless  used  in  such  quan- 
tity as  to  destroy  at  the  same  time  the  roots  of  the  plants;  and  thus 
is  practically  useless,  except  for  disinfecting  soils.  The  very  exhaustive 
and  unsuccessful  experiments  made  with  the  phylloxera,  especially  in 
France,  make  it  appear  doubtful  if  anything  completely  effective  will 
ever  be  found  in  the  way  of  treatment  for  root  insects. 

The  solution  of  the  problem  for  trees  and  vines  seems  to  be  along  the 
line  of  the  use  of  resistant  roots.  Very  satisfactory  resistants  for  the 
phylloxera  of  the  grapevine*  and  for  the  woolly  aphis  of  the  apple  are 
now  on  the  market.  In  regions  where  these  insects  are  troublesome, 
new  plantations  should  not  be  made  except  upon  these  roots. 

For  annual  crops,  the  most  promising  methods  at  present  known  are 
crop  rotation,  starvation,  and  trapping. 

The  crop  rotation  method  depends  for  its  success  upon  the  fact  that 
most  of  the  injurious  root-feeding  insects  or  worms  are  decidedly  more 
numerous  in  a  certain  field  in  certain  years,  and  especially  after  certain 
crops.  By  planting  only  those  crops  that  are  the  least  injured  by  the 
attacks,  in  the  years  following  these  crops,  the  injury  can,  to  some 
degree,  be  avoided.  Local  experience  will  show  the  particular  system  of 
rotation  which  will  give  the  best  results  with  the  insects  that  are  most 
abundant  in  that  particular  region. 

The  starvation  method  is  by  clean  fallowing  the  land,  and  is  not 
particularly  useful  after  a  crop  like  potatoes,  where  considerable  living 
vegetable  matter  is  left  in  the  soil.  It  is  the  most  thorough  method  if 
everything  is  kept  off  the  ground,  and  can  be  used  to  advantage  in 
connection  with  trapping. 

The  trapping  method  consists  of  providing  food  for  the  insects  which 
has  first  been  treated  with  a  strong  dose  of  poison.  It  is  especially 
useful  in  gardens  where  root-feeding  insects  are  often  a  very  serious 
pest.  Any  green  food  will  do  for  traps.  Alfalfa  is  commonly  used.  It 
is  scattered  around  in  small  piles  and  may  be  partly  covered  with  soil 
to  prevent  it  from  drying  out  too  fast. 

There  are  a  few  exceptional  cases  where  a  treatment  can  be  made 
which  will  do  some  good.  The  woolly  aphis  of  the  apple  tree,  for 
instance,  produces  great  excrescences  on  the  trunk  just  below  the 
surface  of  the  ground;  resulting  from  the  attempts  of  the  tree  to  sucker 
and  the  production  of  swellings  on  these  insipient  suckers.  These 
irregular  swellings  very  easily  become  infested  by  toadstool  fungi   and 


*  Bulletin  No.  148,  Calif.  Agr.  Exp.  Station. 


—  6  — 

then  the  fate  of  the  tree  is  sealed.  The  use  of  wood  ashes  about  the 
crown,  while  it  may  kill  any  small  rootlets  at  this  point,  will  not  injure 
the  tree  as  a  whole,  and  will  prevent  the  insects  from  living  at  this  part 
of  the  tree. 

When  the  attack  of  root-feeding  insects  is  not  too  severe  the  plant 
may  not  suffer  very  much,  especially  if  it  is  otherwise  in  the  best  of 
condition  and  has  plenty  of  water.  The  plant  would  in  such  case 
simply  replace  the  destroyed  members  and  there  may  be  scarcely  an 
appreciable  decrease  in  crop. 

Some  of  the  root-feeding  insects,  especially  the  plant-lice,  which 
produce  swellings  in  the  roots,  are  followed  by  another  complication. 
These  swellings  are  liable  to  become  affected  with  rot  organisms. 
Certain  varieties  of  plants  are  more  subject  to  this  trouble  than  others, 
and  some  regions  also  appear  more  subject  to  it,  probably  on  account 
of  climatic  conditions.  This  is  undoubtedly  the  principal  reason  why 
the  woolly  aphis  is  so  fatal  in  Australia,  and  why  it  is  here  often  so 
fatal  to  the  pear. 

A  sucking  insect  can  do  scarcely  any  injury  to  a  healthy  plant  when 
attacking  the  roots,  unless  some  complications  like  the  above  arise,  or 
unless  the  plant  is  allowed  to  suffer  from  want  of  cultivation  or  other 
such  causes.  With  no  other  class  of  insects  is  good  care  more  essential 
as  a  means  of  preventing  injury. 

BORING    INSECTS. 

About  the  only  thing  that  can  be  done  for  boring  insects  is  to  prevent, 
by  some  means,  their  entrance  into  the  plant.  This  may  be  done  by 
mechanical  means,  by  covering  the  threatened  parts  with  something 
which  will  either  prevent  the  egg-laying,  or  which  will  form  a  barrier 
to  the  ingress  of  the  young  insect.  In  many  cases  schemes  of  this  nature 
that  have  seemed  to  promise  well  have  not  proven  effectual  in  actual 
practice.  Thus,  cylinders  of  wire  mosquito  net,  an  inch  or  two  larger 
than  the  trunks  of  the  trees,  have  been  recommended  as  an  effectual  bar 
against  the  borer  that  attacks  the  butts  of  peach  trees.  In  reality  this 
insect  will  lay  its  eggs  above  the  trap,  and  the  mesh  of  the  net  is  far 
too  coarse  to  exclude  the  young  worms.  Again,  the  coating  of  the  plant 
with  a  poisonous  substance  often  fails,  because  of  the  entrance  of  the 
insect  into  cracks  caused  by  the  expanding  bark.  It  would  not  do 
to  encase  the  tree  in  a  coating  that  would  prevent  this  expansion.  It 
would  also  be  fatal  to  so  coat  any  green  part  as  to  prevent  the  normal 
transpiration  of  the  plant.  Nothing  likewise  could  be  used  on  any  part 
of  the  plant  that  would  penetrate  into  the  living  cells.  The  mechanical, 
or  barrier  methods,  therefore,  should  be  carefully  tested  before  being 
used  extensively. 

Insects  like  the  codling-moth  which  bore  into  the  fruit,  can  be  very 
successfully  treated,  because  of  their  habit  of  feeding  for  some  time  on 


'  / 


—  7  — 

the  surface  of  the  fruit  before  entering;  and  the  peach  moth  spends  a 
considerable  part  of  its  life  making  a  series  of  small  burrows  in  the 
bark  of  the  twigs  and  branches,  thus  offering  a  number  of  opportuni- 
ties to  kill  it.  Likewise  the  plum  curculio  of  the  Eastern  States  feeds 
for  some  time  upon  the  plant  before  laying  its  eggs,  and  so  may  be 
killed  and  the  egg-laying  prevented. 

After  the  insects  have  entered  the  plant,  about  the  only  thing  remain- 
ing to  be  done  is  to  dig  them  out  one  by  one;  though  for  some  living 
very  near  the  surface  it  is  said  that  scalding  hot  water,  applied  freely 
to  the  trunk,  will  destroy  the  insect  without  injury  to  the  tree. 

It  is  doubtful,  however,  if  by  either  of  these  means  enough  injury  is 
not  directly  or  indirectly  done  to  the  plant  to  more  than  equal  the  good 
attained. 

Recently  carbon  bisulfid  and  hydrocyanic  acid  gas  have  been  used 
with  remarkably  good  results.  The  use  of  these  substances  is  as  yet 
limited  to  a  few  cases,  such  as  trees  valuable  enough  to  permit  of  rather 
expensive  work,  or  where  the  injury  is  limited  to  a  small  area,  as  in  the 
peach-tree  borer.* 

The  amount  of  injury  resulting  from  the  attacks  of  borers  is  most 
variable,  and  has  no  relation,  in  most  cases,  to  the  amount  of  sub- 
stance devoured  by  the  insect.  In  no  case  is  the  injury  due  to  the 
quantity  of  substance  eaten,  but  usually  results  from  a  disturbance  of  the 
connection  between  the  top  and  the  roots.  In  the  case  of  annual  plants 
the  amount  of  tissue  eaten  at  one  point  is  so  large  that  there  is  not 
enough  left  to  carry  an  adequate  supply  of  sap  to  the  top;  therefore  it 
withers  and  dies.  If  the  same  amount  of  tissue  had  been  removed,  but 
extended  over  twice  the  distance  on  the  stem,  no  injury  might  ha.ve 
resulted.  The  plant  is  always  provided  with  more  of  every  tissue  than 
is  really  needed  by  it,  as  a  provision  against  emergencies.  A  plant 
therefore  that  is  injured  by  a  borer,  if  the  injury  is  not  too  severe,  may, 
if  the  other  conditions  are  favorable,  produce  just  as  good  a  crop,  but  it 
is  less  able  to  pass  through  trying  experiences;  and  the  same  may  be 
said  of  almost  all  kinds  of  plant  diseases.  The  constitution  has  simply 
been  undermined. 

Borers  attacking  small  twigs  sometimes  eat  out  so  much  that  the  twig 
is  no  longer  strong  enough  to  resist  the  beating  of  the  wind,  and  is 
broken  off  in  the  gale.  It  is  generally  better,  in  such  cases,  that  the 
twig  be  so  broken  off  that  the  plant  may  immediately  replace  it,  because 
it  will  take  the  twig  a  long  time  to  heal  up  and  make  good  such  an 
injury.  The  injury  to  the  plant  in  this  case  consists  not  so  much  in 
the  loss  of  the  twig  as  in  the  time  at  which  the  twig  is  removed;  which 
is  often  such  as  to  disarrange  the  plans  or  rather  the  conditions  of  the 
plant  in  regard  to  pruning,  in  such  a  way  that  it  is  not  possible  to 


*  Bulletin  No.  143,  Calif.  Agr.  Exp.  Station. 


—  8  — 

secure  the  condition  most  favorable  to  the  setting  and  maturing  of  the 
crop.  The  loss  of  a  few  twigs,  of  course,  amounts  to  nothing,  but  if 
many  twigs  in  a  tree  are  affected,  a  serious  disarrangement  in  the  con- 
dition of  the  tree  may  result. 

Borers  in  the  trunk  of  the  tree  menace  its  health  in  another  way. 
Here,  whatever  injury  is  done  results  almost  wholly  from  the  destruction 
of  the  growing  layer  of  tissue  just  beneath  the  bark.  The  holes  made 
in  the  heart-wood  produce  no  injury,  except  to  its  value  as  timber;  but 
the  destruction  of  the  growing  tissue  beneath  the  bark  is  dangerous  in 
that,  if  the  dead  spot  is  of  large  enough  extent,  the  wood  immediately 
beneath  it  may  dry  out  and  reduce,  by  just  that  much,  the  water-carrying 
power  of  the  trunk.  The  tree  thus  becomes  less  able  to  withstand 
drought.  If  the  dead  tissue  is  extensive  enough,  the  trunk  may  so  dry 
out  that  the  top  will  die  for  want  of  water,  even  though  there  is  plenty 
in  the  soil.  If  the  tree  is  protected  with  grafting  wax  until  the  wounds 
made  by  borers  have  time  to  heal  over,  no  bad  results  will  usually 
follow. 

SAP-SUCKING    INSECTS. 

In  this  category  are  included  some  of  the  easiest  as  well  as  some  of 
the  most  difficult  insects  to  destroy,  but  they  are  all  capable  of  successful 
treatment,  so  far  as  we  know.  It  may  often  be,  however,  that  the  cost 
of  a  treatment  which  is  effective  will  be  so  great  as  to  be  prohibitive. 
This  is  true  generally  of  field  crops,  where  the  cost  per  acre  for  treatment 
may  often  be  more  than  the  saving  that  can  ensue  from  the  application- 
The  insects  of  this  class  are  not  affected  by  poisons  like  paris  green, 
because  they  get  their  food  by  inserting  their  beak  into  the  plant;  nothing, 
therefore,  on  the  surface  of  the  leaves  will  have  any  preventive  effect. 

There  have  been  many  attempts  to  inject  some  substance  into  the 
plant  which  will  poison  the  sap;  but  the  cells  of  the  plant  are,  if  any- 
thing, more  delicate  than  the  insect,  so  that  the  plant  is  always  killed 
first. 

The  only  feasible  plan,  therefore,  is  to  spray  on  the  plants  some 
caustic  or  oily  substance,  or  to  envelop  them  with  some  poisonous  gas. 

Plant-lice  are  ordinarily  very  easy  to  kill,  but  protected  insects  like 
the  scales,  or  very  active  ones  like  the  so-called  grape  thrips,  are  much 
more  difficult  to  deal  with.  The  latter  are  probably  best  treated  by 
causing  them  to  leap  or  fly  against  a  "hopper-dozer"  of  some  form, 
catching  them  as  they  drop  to  the  ground  in  the  evening,  or  early  in  the 
morning;  or  in  nets.*  The  "hopper-dozer"  is  the  name  applied  to  any 
surface  coated  with  any  substance  fatal  to  the  insect,  and  against  which 
the  insect  is  made  to  jump  or  fall.  For  such  an  insect  as  the  vine 
hopper  a  palm  leaf  fan  makes  a  very  convenient  form  of  dozer. 


*  Bulletin  No.  116,  Calif.  Agr.  Exp.  Station, 


/*  1 

—  9  — 

There  is  the  greatest  amount  of  misconception  as  to  the  nature  of  the 
injury  produced  by  sap-sucking  insects.  Except  during  dry  spells,  or 
when  the  numbers  are  excessive,  or  when  they  attack  particular  parts 
of  the  plant,  the  injury  they  do  is  scarcely  worth  considering.  Under 
these  adverse  conditions,  however,  they  are  often  fatal  to  the  plant.  No 
other  class  of  injury  renders  a  plant  less  able  to  successfully  pass 
through  a  drought  than  does  that  caused  by  sucking  insects ;  in  an  arid 
climate  like  that  of  California  the  summer  is  all  droughty,  and  that 
is  one  reason  why  they  are  so  injurious  with  us.  A  plant  has  the  means 
of  lessening  the  rate  of  evaporation  during  the  dry  part  of  the  day,  and 
can  thus  thrive  in  comparatively  dry  conditions;  but  if  infested  by 
sucking  insects  it  loses  water  at  a  rapid  rate  to  supply  the  necessities  of 
the  insects  preying  upon  it.  The  result  is  the  same  as  though  the 
drought  was  much  more  severe;  the  leaves  ripen  and  drop  prematurely, 
and  the  young  growth  becomes  sunburned  and  dries  up,  and  the  whole 
plant  may  die.  The  insects  of  this  class  often  reproduce  very  rapidly, 
and  so  become  very  numerous;  no  plant  can  withstand  an  overwhelm-  • 
ing  attack. 

The  injury  to  certain  parts  of  the  plant  is  often  quite  serious.  Thus, 
very  commonly,  the  attack  will  be  concentrated  upon  the  growing  tip 
of  the  twig  and  prevent  its  healthy  and  normal  growth.  In  this  way 
the  plant  may  be  prevented  from  making  the  necessary  amount  of  foliage 
during  the  time  when  the  conditions  are  favorable  to  its  production, 
and  the  injury  will  be  greater  than  is  apparent.  Some  insects  at  times 
confine  their  attack  to  the  bud,  or  young  fruit  or  seed,  and  cause  its 
dropping  or  imperfect  development.  This  injury  may  not  seriously 
damage  the  plant  as  a  plant,  and  yet  may  destroy  its  profitableness  as 
a  crop  producer. 

In  certain  species  the  control  is  made  more  difficult  by  the  distortion 
of  the  undeveloped  leaves  where  attacked  by  the  lice.  The  curled 
leaves  which  result,  form  a  perfect  protection  for  the  insects  against  any 
spray  that  might  be  used.  In  these  cases  the  application  must  be 
made  before  any  of  the  leaves  have  become  curled. 

A  secondary  injury  is  sometimes  produced  by  the  growth  of  a  fungus 
on  the  excretion  of  these  insects,  as  in  the  case  of  the  smut  fungus  on 
citrus  fruits,  which  may  so  disfigure  the  fruit  as  to  cause  very  serious 
loss. 

DEFOLIATING    INSECTS. 

The  insects  eating  the  leaves  of  plants  are,  as  a  rule,  the  easiest  to 
destroy,  and  at  the  least  expense,  because  the  leaves  may  be  covered 
with  relatively  cheap  poisonous  substances;  and  as  the  insects  eat  the 
leaf,  they  will  also  consume  the  poison  and  be  killed.  Only  the  more 
valuable  field  crops  can  be  thus  treated  economically,  however,  for  even 
as  cheap  a  process  as  this  is  too  expensive  for  most  of  the  staple  crops. 
cir.  no.  7 


—  10  — 

When  insects  are  excessively  abundant,  as  in  the  case  of  attacks  of 
swarms  of  locusts  and  invasions  of  army  worms,  all  known  applica- 
tions become  useless,  because  with  their  great  numbers  everything  green 
is  devoured  before  any  one  insect  can  have  taken  enough  poison  to 
kill  it. 

The  use  of  a  mixture  of  bran,  molasses,  and  arsenic,  or  horse  manure 
and  arsenic,  both  of  which  seem  to  be  preferred  even  to  foliage  by  the 
insects,  sometimes  does  good  service  if  the  number  of  the  insects  is  not 
too  great,  and  the  poison  is  placed  on  their  way  to  the  unattacked 
territory.* 

Insects  of  the  defoliating  class  can  also  be  killed  by  the  same  reme- 
dies that  are  used  for  sap-sucking  forms;  but,  as  in  the  case  of  the  latter 
class,  the  insect  must  actually  be  touched  by  the  remedy  to  be  affected 
by  it. 

Often  it  will  be  found  that  the  use  of  other  measures  is  more  profit- 
able than  spraying.  The  use  of  barriers  is  the  most  effectual  against 
certain  insects  of  this  class.  Climbing  cut-worms  can  be  prevented 
from  ascending  trees,  by  taking  a  piece  of  cotton-batting  about  ten 
inches  wide  and  long  enough  to  lap  about  two  inches,  wrapping  it 
around  the  trunk  of  the  tree,  tying  it  fast  by  means  of  a  string  near 
the  lower  edge  and  then  pulling  the  upper  edge  down  over  it  like  an 
inverted  funnel.  The  use  of  a  sticky  substance  painted  on  a  strip  of 
paper  around  the  tree  also  prevents  the  passing  of  any  insect  that  gets 
on  the  tree  by  crawling  up  the  trunk.  The  use  of  the  paper  is  to  pre- 
vent injury  to  the  bark  that  may  be  caused  by  the  penetration  of  the 
substance  used  as  a  barrier. 

The  jarring  of  insects  onto  hopper-dozers,  or  on  sheets  from  which 
they  may  be  gathered  and  destroyed,  is  effectual  against  some  insects. 
The  ordinary  insect  net  is  the  best  thing  that  can  be  used  for  some,  and 
especially  for  the  active  flying  species.  Hand-picking  is  by  no  means 
to  be  despised,  and  in  many  cases  (but  generally  on  a  small  scale)  is 
the  most  economical  proceeding.  This  is  especially  true  for  large 
insects  and  for  those  that  are  gregarious;  they  may  often  be  con- 
veniently shaken  down  into  a  vessel  containing  a  Jittle  coal  oil. 

The  injury  done  by  defoliating  insects  depends  almost  wholly  on  the 
time  of  their  attack.  If  done  late  in  the  year  it  may  not  be  at  all 
serious.  The  greatest  injury  is  generally  done  if  the  leaves  are  taken 
off  while  the  crop  is  being  produced.  If  late  in  the  spring  both  the 
crop  and  the  plant  are  in  danger;  and  chiefly  the  crop  if  earlier.  This 
kind  of  injury  is  so  evident  that  one  is  not  likely  to  make  a  wrong 
estimate  of  its  amount. 


*  Bulletin  No.  142,  Calif.  Agr.  Exp.  Station. 


—  11  — 

REMEDIES  AGAINST  INSECTS. 

There  are  a  great  many  substances  that  may  be  used  successfully 
against  insects;  but  we  recommend  only  a  small  list,  selected  because 
of  their  effectiveness  and  cheapness.  Remedies  are  applied  as  a  dry 
powder,  as  a  gas,  or  as  a  fluid  spray  or  wash;  the  great  majority  being 
in  the  latter  form. 

POWDERS. 

The  most  common  way  of  applying  powders  is  the  "  pepper-box " 
method,  in  which  the  material  is  carried  in  a  vessel  provided  with  per- 
forations, through  which  it  sifts  as  the  vessel  is  shaken  over  the  plant. 
A  modification  of  this,  much  used  in  the  cotton  fields  of  the  Southern 
States,  consists  of  bags  of  the  material  suspended  from  the  ends  of  a 
pole  long  enough  to  reach  from  one  row  of  cotton  to  the  next.  This  is 
carried  by  a  man  riding  on  a  mule,  and  the  jar  causes  the  powder  to 
sift  through.  Cloth  is  chosen  for  this  purpose,  which  is  fine  enough  to 
allow  only  the  right  quantity  to  be  distributed.  A  third  method,  much 
used  in  this  country,  is  a  blowing  device,  which  is  very  satisfactory  for 
field  use,  and  does  very  rapid  work.  Only  three  remedies  are  recom- 
mended to  be  used  in  the  dry  form,  and  these  have  a  rather  limited  use. 

Air- Slaked  Lime. — This  is  the  powder  resulting  from  the  exposure  of 
ordinary  lime  to  the  action  of  the  air  for  some  time.  It  is  only  recom- 
mended as  a  remedy  against  insects  which  have  a  slimy  coating  over 
the  body.  For  these  it  is  cheap  and  effectual.  It  is  not  as  cheap,  how- 
ever, as  paris  green,  and  is  particularly  recommended  where  the  latter 
is  objectionable  because  of  its  poisonous  nature.  The  cherry  slug,  for 
instance,  often  attacks  the  plant  even  as  late  as  picking  time,  and  paris 
green  should  not  be  applied  later  than  two  weeks  before  picking.  The 
action  of  the  lime  is  on  the  glands  of  the  skin  that  secrete  the  slime, 
and  so  is  only  fatal  to  slimy  creatures.  For  true  slugs,  which  are  not 
insects,  but  have  a  similar  slimy  coat,  it  is  the  best  remedy  we  know 
of;  but  it  must  be  applied  in  the  evening  or  early  morning,  while  the 
animals  are  on  the  plants;  and  may  have  to  be  repeated  two  or  three 
nights  in  succession  to  kill  all.  Except  in  gardens,  it  may  not  pay  to 
make  more  than  the  one  application,  which  will,  if  rightly  timed, 
destroy  most  of  the  slugs. 

Sulfur. — This  is  a  widely  used  remedy  for  certain  fungous  diseases, 
and  it  has  likewise  been  found  to  be  a  successful  remedy  for  the  so-called 
red  spider,  also  called  yellow  mite— animals  somewhat  related  to  the 
true  insects;  fairly  good  results  are  also  reported  in  its  use  against  the 
thrips.  For  these  purposes  the  sulfur  is  used  in  the  same  way  as  for 
the  mildew. 

The  powder  is  usually  applied  by  the  pepper-box  method.  It  only 
becomes  effectual  as  the  heat  of  the   sun  vaporizes  it;  the  field  thus 


—  12  — 

treated  smells  strongly  of  the  sulfur  during  the  warmer  part  of  the  day, 
when  the  vapor  is  being  produced.  On  wet,  cloudy  days  the  sulfur  is 
inert,  but  the  first  bright  day  makes  it  effective.  It  may  be  possible  to 
artificially  vaporize  the  sulfur  on  a  large  scale  for  use  in  such  weather; 
but  no  attempt  has  yet  been  carefully  made,  except  in  greenhouses,  and 
then  with  the  best  of  results.  The  vapor  of  sulfur  must  be  used,  and 
not  the  gas  produced  by  burning,  which  is  very  injurious  to  foliage. 

There  are  two  forms  of  sulfur  used  for  these  purposes,  the  ground 
and  the  sublimed  or  flowers  of  sulfur,  and  are  about  equally  pure,  but 
the  nodular  projections  of  the  latter,  allowing  it  to  catch  on  the  rough 
places  on  the  leaf,  make  it  possible  to  produce  the  effect  desired  with  a 
considerably  weaker  application.  The  saving  here  is  about  enough  to 
compensate  for  the  difference  in  price.  At  the  same  time,  the  sublimed 
sulfur  is  more  apt  to  contain  some  sulfuric  acid,  and  when  it  does,  it 
may  injure  the  foliage  if  not  applied  evenly  or  if  applied  too  thickly. 
One  can  recognize  the  presence  of  the  acid  by  the  sour  taste,  and  sulfur 
that  is  sour  should  be  avoided.  When  sulfur  is  burned,  the  fumes  are 
very  injurious  to  plant  life,  because  they  become  sulfuric  acid  on  combin- 
ing with  the  water  and  oxygen  of  the  air  or  plant. 

Paris  Green  or  Other  Arsenicals. — The  arsenical  poisons  while  occa- 
sionally used  in  a  dry  form,  are  more  commonly  suspended  in  water  to 
be  used  as  a  spray.  They  are  used  for  the  same  purposes  in  either  form. 
A  common  practice  is  to  dilute  the  poison  with  flour,  dust,  or  other 
powder,  so  that  it  can  be  more  easily  and  evenly  distributed.  If  not 
so  diluted,  care  must  be  taken  not  to  apply  it  so  thickly  in  places  as  to 
endanger  the  foliage. 

GAS   TREATMENTS. 

Gases  have  the  property  of  diffusing  themselves  with  great  rapidity, 
so  that  when  applied  in  a  closed  space,  every  part  of  that  space  will  in 
a  short  time  contain  some  of  the  gas.  Thus,  no  other  method  of  killing 
insects  is  calculated  to  be  as  thorough  in  its  work.  In  an  open  space 
this  property  of  diffusing  destroys,  to  a  great  extent,  its  utility.  Sulfur 
applied  as  a  powder,  as  has  already  been  stated,  is  not  effective  until  it 
becomes  a  vapor;  and  then  the  dissipation  is  not  as  much  as  with  most 
gases,  because  of  the  weight  of  sulfur  vapor  and  the  fact  that  it  is 
applied  over  whole  fields  at  once. 

The  impracticability  of  inclosing  most  cultivated  plants,  and  the  cost 
of  the  treatment,  both  in  time  and  chemicals,  make  the  method  useful 
to  only  a  very  limited  extent.     We  recommend  but  two  gases. 

Carbon  Bisulfid. — This  substance  is  not  available  for  plants,  or  rather 
the  parts  of  plants  in  active  growth,  and  is  chiefly  used  for  stored  prod- 
ucts, such  as  seeds  and  grains.  It  can  be  used  for  disinfecting  soils 
and  ridding  other  articles  of  insects. 


—  13  — 

In  disinfecting  soils  an  injector  is  used.  A  number  of  forms  of  the 
latter  are  on  the  market  in  Europe,  where  phylloxera  eradication  has 
required  them.  It  is  doubtful  if  this  method  of  soil  disinfection  would 
be  profitable  in  this  country  for  the  destruction  of  any  insect. 

For  destroying  insects  in  seeds  or  grain,  carbon  bisulfid  is  a  very 
cheap  and  satisfactory  means.  The  bin  or  box  containing  the  seeds  to 
be  disinfected  should  be  tight,  at  least  at  the  sides  and  below. 

A  dish  is  placed  on  top  of  the  material  to  be  treated,  and  a  quantity 
of  the  carbon  bisulfid  poured  in.  This  evaporates  rapidly,  and  the 
vapor  being  heavier  than  the  air,  sinks  down  into  the  lower  part  of  the 
bin.  The  top  should  be  covered  also,  in  order  that  the  vapor  may 
remain  a  long  time  in  the  grain. 

Very  rarely  will  bins  be  perfectly  tight,  so  that  the  exact  amount 
necessary  can  not  be  stated.  Usually  the  estimate  is  made  at  one 
pound  to  the  ton  of  grain,  which  is  sufficient  for  a  fairly  tight  bin. 

Grapevine  cuttings  are  most  successfully  disinfected  in  a  similar  way, 
by  placing  a  saucerful  of  the  bisulfid  on  the  cuttings  in  a  tight  box,  and 
leaving  for  forty  minutes. 

The  yellow-jacket,  our  common  wasp,  which  is  so  injurious  to  fruit, 
and  which  makes  its  nest  in  the  ground,  is  easily  killed  by  this  sub- 
stance. The  nest  is  located,  and  about  dark,  when  the  wasps  are  all  in, 
about  an  ounce  of  carbon  bisulfid  is  poured  down  the  hole  and  a  hand- 
ful of  earth  thrown  over  it  to  keep  the  vapor  in.  By  morning  all  will 
be  found  to  be  dead.     Ants'  nests  can  be  destroyed  in  the  same  way. 

Carbon  bisulfid  is  also  one  of  the  best  remedies  for  gophers  and 
ground  squirrels.  If  used  in  the  fall,  after  the  rains  have  begun  (so 
that  the  ground  is  not  too  porous),  an  ounce  poured  over  a  rag  and 
stuffed  into  a  hole  and  covered  with  earth  will  destroy  the  inmates. 

Recently  carbon  bisulfid  has  been  successfully  used  for  destroying  the 
root-crown  borer  of  the  peach  in  Santa  Clara  County.  Except  where 
the  soil  is  very  permeable  a  trench  should  be  dug  around  the  trunk 
and  the  surface  soil  scraped  in  until  it  is  level,  and  then  about  an  ounce 
of  the  bisulfid  poured  around  and  the  earth  mounded  slightly  to  retain 
the  fumes.  If  the  soil  is  very  dry  much  greater  quantities  would  have 
to  be  used,  and  if  wet  there  is  danger  to  the  tree  if  the  chemical  is 
allowed  to  remain  too  long.  It  is  good  policy  to  remove  the  earth  if 
an  appreciable  quantity  of  gas  remains  after  two  days.  When  the  soil 
is  moist  care  must  be  had,  when  digging  the  trench,  not  to  glaze 
over  any  of  the  soil  next  to  the  tree,  or  the  gas  will  be  effectually  kept 
out  of  the  burrows  and  the  insects  will  not  be  killed.  The  soil  condi- 
tion is  the  most  important  consideration  in  this  treatment.* 

Hydrocyanic  Acid  Gas. — This  is  practically  the  only  gas  which  is 
strong  enough  to  kill  the  insects  on  a  tree  with  safety  to  the  leaves,  and 


*  Bulletin  No.  143,  Calif.  Agr.  Exp.  Station. 


—  14  — 

within  a  time  short  enough  to  make  its  use  practical  on  a  large  scale. 
Its  work  is  very  effectual  and  satisfactory,  but  is  very  expensive,  and, 
therefore,  is  only  available  for  the  more  profitable  trees,  such  as  the 
citrus  varieties.  It  may  also  be  used  for  disinfecting.  The  gas  is 
extremely  poisonous,  and,  sometimes,  for  reasons  not  entirely  under- 
stood, is  very  injurious  to  the  foliage;  but  the  injury  is  almost  all 
prevented  by  its  use  at  night. 

The  process  is  to  cover  the  tree  with  a  tent  of  sail-cloth,  often  oiled  to 
make  it  tight,  and  in  a  vessel  beneath  the  tent  the  chemicals  which 
make  the  gas  are  placed.  About  fifty  minutes  is  considered  necessary 
for  effective  work.  The  original  recommendation  was  an  ounce  of 
potassium  cyanide  for  150  cubic  feet. 

The  common  practice  in  this  State  is  to  use  it  decidedly  stronger  for 
small  trees  and  weaker  for  the  largest  trees.  In  the  smaller  trees  it  is 
safe  to  use  it  stronger,  as  the  small  amount  of  gas  used  is  very  quickly 
diffused.  When  it  is  produced  in  large  quantity,  as  is  necessary  for  a 
large  tree,  some  of  the  gas,  scarcely  at  all  mixed  with  air,  may  come  in 
contact  with  the  leaves  and  injure  them.  The  leakage  of  gas  in  the 
tents  commonly  used  is  so  great  that  the  dose  should  be  proportioned  to 
some  extent  upon  the  area  of  the  tent  surface.  The  whole  matter  is  so 
complicated  that  we  can  not  attempt  to  discuss  it  here,  but  will  refer  to 
a  recent  bulletin  on  the  subject.* 

For  disinfecting  nursery  stock,  seeds,  or  anything  not  growing,  it  is 
possible  to  increase  both  the  dose  and  the  time  of  treatment.  The 
formula  is  one  part  by  weight  of  potassium  cyanide  to  a  mixture  of  one 
part  of  sulfuric  acid  and  two  parts  of  water,  both  by  volume.  Upon 
adding  the  cyanide  to  this  diluted  acid  there  is  an  immediate  evolution 
of  gas.  The  greatest  caution  should  be  exercised  in  handling  these 
chemicals  and  particularly  should  one  be  careful  not  to  breathe  the  gas 
as  it  is  being  generated. 

SPRAYS    OR   WASHES. 

The  most  important  remedies  for  plant  pests  are  applied  as  sprays  or 
washes.  By  the  word  washes  one  would  naturally  understand  a  more 
copious  application  than  a  spray,  but  in  ordinary  usage  the  terms  are 
identical. 

For  very  low  plants  an  outfit  working  on  the  principle  of  a  sprinkling- 
can  will  do;  but  for  better  and  more  economical  work,  and  work  on 
taller  plants,  some  form  of  force-pump  or  spray-nozzle  is  necessary. 

There  are  many  forms  of  pumps  on  the  market  that  are  good  for  the 
purpose.  A  good  spray  pump  should  maintain  a  fairly  constant  and 
sufficient  pressure,  and  its  valves  and  general  construction  should  be 
simple,  and  its  parts  easily  replaceable. 


*  Bulletin  No.  152,  Calif.  Agr.  Exp.  Station. 


—  15  — 

The  nozzle  should,  for  most  spraying  work,  be  such  as  to  break  up 
the  stream  into  a  fine  mist;  but  for  scale  insects  one  giving  a  stream  of 
considerable  force  is  desirable.  The  shape  of  the  spray  is  usually  either 
conical  or  fan-shaped,  and  each  has  its  particular  advantages  for  its 
own  class  of  work. 

The  construction  of  the  nozzle  should  be  such  as  to  permit  of  easy, 
quick,  and  thorough  cleaning.  A  few  forms  designed  to  clean  them- 
selves automatically,  work  well. 

In  most  spraying,  the  object  is  to  get  the  largest  possible  proportion 
of  the  spray  to  remain  on  the  leaf  or  stem,  and  to  have  it  well  dis- 
tributed. This  is  best  accomplished  by  covering  the  leaf  with  minute 
globules  like  dew.  As  soon  as  they  run  together  and  drip  from  the  leaf 
the  distribution  is  not  perfect,  and  there  is  actually  less  left  on  the 
leaves. 

When  the  nozzle  is  held  as  far  from  the  plant  as  the  stream  will 
carry,  the  full  effect  of  the  nozzle  is  obtained  in  the  breaking-up  of  the 
stream  into  mist,  and  so  can  produce  most  perfectly  this  dew-like 
condition. 

For  scale  insects  the  object  is  somewhat  different.  The  plan  for  these 
is  to  thoroughly  wet  the  surface  of  the  bark  and  the  edges  of  the  scale, 
to  insure  the  penetration  of  the  wash  beneath  the  scale,  and  thus  to 
kill  the  old  scale,  or  the  eggs  and  young  hidden  beneath.  This  thorough 
wetting  is  secured  by  holding  the  nozzle  close  to  the  plant  and  apply- 
ing a  great  deal  of  wash  with  a  high  pressure.  Washes  are  sometimes 
applied  hot,  and  when  the  nozzle  is  held  close  to  the  plant  the  spray 
will  penetrate  better,  and  for  this  reason  will  do  better  work. 

Lime,  Salt,  and  Sulfur  Mixture. — This  mixture  is  of  California  origin 
and  is  considered  the  best  remedy  for  the  San  Jose  scale  and  for  peach 
worm,  as  well  as  for  certain  fungi,  particularly  the  curl  leaf  of  the 
peach.*  It  is  also  very  efficient  in  softening  and  smoothing  up  old 
rough  bark.  The  formula  most  extensively  used  is  40  pounds  of  lime, 
20  pounds  of  sulfur,  and  15  pounds  of  salt,  with  enough  water  to  make 
60  gallons. 

The  sulfur,  about  a  third  of  the  water,  and  a  quarter  of  the  lime  are 
boiled  together  for  an  hour  and  a  half  or  two  hours.  The  salt  and 
the  remainder  of  the  lime,  after  slaking,  are  mixed  separately  and  finally 
added  to  the  lime-sulfur  mixture  and  the  whole  boiled  another  half 
hour.  The  mixture  requires  careful  straining  to  prevent  clogging  in 
the  nozzle.     It  should  be  applied  hot  and  in  good  quantity. 

Sulfid  of  Potash  Wash. — This  mixture  was  found  very  effective  against 
red  spider.f     The  formula  is  32  pounds  of  potash,  37  pounds  of  sulfur, 


*  Bulletin  No.  144,  Calif.  Agr.  Exp.  Station. 
t  Bulletin  No.  145,  Calif.  Agr.  Exp.  Station. 


—  16  — 

and  5  pounds  of  salt,  and  water  to  make  about  500  gallons  of  wash. 
The  ingredients  are  placed  together  with  a  very  small  amount  of  water, 
when  a  violent  chemical  reaction  at  once  sets  in.  After  this  has  sub- 
sided the  mixture  is  diluted  to  the  desired  extent. 

Resin  Soap. — The  cheapest  insecticide  which  kills  by  contact  is  resin 
soap.  It  is  for  scale  insects,  and  has  good  penetrating  power.  Like  all 
insecticides  which  kill  by  contact,  the  effect  of  the  spray  is  soon  gone, 
and  it  only  kills  the  insects  which  are  wet  with  its  spray.  It  is  generally 
applied  warm. 

In  making  the  soap,  the  ingredients  are  placed  in  a  closed  kettle  with 
enough  water  to  cover,  and  are  boiled  for  two  hours,  when  all  will  be 
united  into  a  soap.  In  diluting,  only  a  little  water  should  be  added  at 
a  time,  and  stirred  in;  or,  better,  hot  water  should  be  used,  because  of 
the  danger  of  chilling  the  soap  and  causing  it  to  harden,  when  it  is 
almost  impossible  to  dissolve  it  again. 

The  proportions  are  8  pounds  of  resin,  2  pounds  of  standard  caustic 
soda,  and  1  pint  of  fish  oil,  for  40  gallons,  for  use  on  trees  in  foliage; 
and  the  same  for  25  to  30  gallons  for  winter  use. 

Distillates. — Distillates  of  petroleum  have  of  late  years  become  very 
prominent  as  insecticides.  The  safest  of  the  distillates  to  use  on  green 
parts  of  plants  is  ordinary  kerosene.  The  best  manner  of  applying 
these  substances  is  by  means  of  a  mechanical  mixing  device,  of  which 
there  are  many  forms  on  the  market.  A  very  satisfactory  home-made 
mixer  for  a  barrel  is  a  vertical  shaft  with  paddles,  which  may  be  rotated 
by  hand  with  a  crank  or  gearing  at  the  top.  The  amount  of  oil  used 
varies  from  1  to  10  per  cent  for  plants  in  foliage,  only  kerosene  for  the 
latter,  and  from  5  to  25  per  cent  for  dormant  trees.  Different  plants 
will  stand  different  amounts  of  oil.  The  personal  equation  of  the 
sprayer  is  an  important  item,  since  the  oil  accumulates  if  one  continues 
to  spray;  and  thus  it  happens  that  with  the  same  nozzle  and  outfit  one 
person  may  put  as  much  oil  on  a  tree  at  3  per  cent  that  another  would 
apply  at  6  per  cent.  One  should  use  a  nozzle  capable  of  producing  a 
very  fine  mist,  and  the  operation  should  be  stopped  before  the  drops  run 
together  and  drip  from  the  leaves.* 

Kerosene  Emulsion. — While  not  as  cheap  as  the  materials  described 
above,  still  because  of  its  safety  to  the  plant  when  properly  made,  it  is 
valuable  when  a  relatively  small  quantity  of  spray  is  desired. 

The  ordinary  form  of  the  emulsion  is  something  of  an  art  to  properly 
manufacture.  The  ingredients  are  2  parts  of  kerosene  to  1  of  sour  milk, 
or  of  strong  soap  solution.  The  latter  must  be  made  boiling  hot  and 
added  to  the  kerosene,  and  the  whole  pumped  through  a  spray  nozzle 
for  fifteen  minutes.     After  pumping  a  few  minutes  the  whole  mass  will 


*  Bulletin  No.  153,  Calif.  Agr.  Exp.  Station. 


—  17  — 

become  beautifully  creamy  and  apparently  perfectly  emulsified;  but  if 
a  little  is  placed  in  water  it  will  be  seen  that  some  of  the  kerosene  sepa- 
rates out  and  rises  to  the  surface.  The  pumping  must  therefore  be 
continued  to  about  the  time  indicated.  When  the  emulsion  is  perfect 
there  will  be  no  separation  when  diluted.  If  the  soap  is  of  poor  quality 
or  the  water  is  hard,  more  soap  must  be  used;  and,  on  the  other  hand, 
if  both  are  good,  not  as  much  is  needed  as  recommended  below,  which 
is  intended  to  suit  the  average  conditions. 

The  proportions  are  3  ounces  of  soap  in  3  pints  of  water  (or  3  pints  of 
sour  milk)  and  3  quarts  of  kerosene  for  10  gallons  of  emulsion  for  scale 
insects,  or  for  15  gallons  of  emulsion  for  plant-lice. 

Another  formula,  which  is  easier  made  but  more  expensive,  and  so 
only  recommended  for  use  on  a  small  scale,  consists  in  using  eight  times 
as  much  soap.  When  so  made,  the  creamy  mixture  described  above, 
obtained  within  five  minutes,  is  a  permanent  emulsion. 

The  Arsenicals. — These  poisons  are  by  far  the  cheapest  insecticides 
known.  They  are  only  efficient  against  insects  that  eat  the  leaves,  and 
are  useless  for  sucking  insects  or  scales.  They  are  also  useless  against 
overwhelming  numbers  of  insects,  such  as  swarms  of  grasshoppers, 
which  are  able  to  eat  up  the  plant  before  getting  enough  poison  to  kill 
them. 

Arsenic  is  the  active  principle  in  all  these  poisons  and  usually  con- 
stitutes about  one  half  the  substance  of  the  poison.  Paris  green,  which 
is  an  aceto-copper  arsenite,  is  the  most  widely  used  of  all  the  arsenicals,* 
though  several  others  seem  about  equally  satisfactory.  All  forms  of 
arsenicals  should  be  insoluble  in  water,  and  it  is  well  to  use  enough 
lime  or  other  ingredient  which  may  mechanically  protect  the  plant, 
since  there  may  be  otherwise  considerable  danger  of  burning  the  foliage. 

Most  arsenicals  require  constant  stirring,  or  the  material  will  settle 
to  the  bottom,  and  so  not  be  uniformly  distributed.  For  the  best 
results,  the  poison  should  not  be  allowed  to  drip  from  the  tree,  and  the 
finer  the  spray  the  better. 

These  poisons  do  not,  as  a  rule,  remain  any  great  length  of  time  on 
the  plant,  but  must  be  renewed  every  two  or  three  weeks,  or  while  the 
danger  of  insect  attack  exists.  In  mixing  the  poison,  it  is  well  to  first 
make  a  paste  with  a  little  water  and  then  dilute,  as  otherwise  it  is  diffi- 
cult to  wet  the  leaves  with  it.  The  amount  used  is  about  1  pound  to 
200  gallons  of  water. 

When  it  is  desirable  to  use  paris  green  and  Bordeaux  mixture  at  the 
same  time,  as  for  codling-moth  and  scab,  the  green  may  be  stirred  into 
the  Bordeaux  mixture  at  the  usual  proportions,  i.  e.,  1  pound  to  200 
gallons. 


*  Bulletins  Nos.  126  and  151,  Calif.  Agr.  Exp.  Station. 


18  — 


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DIRECTIONS    FOR    SENDING    SPECIMENS. 


The  Experiment  Station  will  give  special  directions  for  specific  insect 
troubles.  Persons  writing  to  the  Station  for  this  purpose  should  always 
forward  at  the  same  time  specimens  of  the  insect  about  which  informa- 
tion is  desired.  These  should  never  be  simply  inclosed  in  the  envelope 
with  the  letter,  as  they  will  almost  invariably  be  crushed,  and  will  often 
be  unrecognizable.  The  best  package  in  most  cases  is  a  light  wooden 
box.  Tin  boxes  are  good,  if  paper  is  placed  within  to  take  up  any 
moisture  that  may  arise.     No  provision  need  be  made  for  ventilation. 


SACRAMENTO 

SHANNON.        -        -       SUPT.     STATE    PRINTING. 
1903. 


